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GFI trips when turning on a computer with the monitor on but not when the monitor is off

Home Improvement Asked by user155292 on December 28, 2020

I have an unusual situation here. I have an older Dell computer that is plugged into an outlet. The monitor that I use with this computer has its own power switch and is also plugged into the same outlet.

If I turn on the computer first and then the monitor, all works okay. However, if I turn on the monitor first and then the computer, a GFCI on a different circuit trips. The neutral wire for this particular outlet is not shared anywhere with the wiring of the other affected circuit except, of course, at the box where all the neutrals are shared. There are additional outlets on this circuit where my Dell is plugged into.

A couple of things to note:

  1. There are several individual circuits coming from the box and because the box is located in a shed away from the house, every circuit has its own GFCI.
  2. Two of the circuits have GFCI breakers while the remaining circuits have GFCI outlets. One of the GFCI breakers is the one that trips.
  3. The computer is plugged into a regular outlet downstream from its GFI outlet.
  4. The separate wires for each of these circuits do run parallel to each other inside the wall.

Michael

One Answer

If the GFCIs have a 5mA threshold, the reason might be related to the cable capacitances. Domestic cables can accumulate 200-400 nanoFarad per kilometer, i.e. the GFCI could trip if the summed up downstream cable length is 500m , if the voltage is 120V, 60Hz. Without any devices plugged into the circuit.

The usual PI-filters of switch mode power supplies in PCs and monitors can add more capacitance, increasing the tripping probability. This is why those 5mA GFCIs seem to be too sensitive in some cases, thus providing not more safety then a 30mA GFCI, but instead are the reason for a safety gap if the annoyed user eliminates that 5mA GFCI if it tripped again just before he was to top his high score in the difficult PC game after weeks of failed sessions.

Answered by xeeka on December 28, 2020

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